This invention relates to a milling cutter of the type in which indexable cutting inserts are removably secured in pockets spaced circumferentially around the periphery of a cutter body. Each cutting insert includes several alternately usable cutting edges. When one cutting edge becomes worn, the insert may be turned or indexed in the pocket in order to bring a fresh cutting edge into active cutting position.
Indexable cutting inserts are available in various shapes. One of the most common inserts is square and includes four cutting edges. Such an insert is especially useful in cases where it is necessary to mill a square or 90-degree shoulder in the workpiece being cut.
Octagonal inserts with eight cutting edges also are widely used. Adjacent cutting edges of such an insert extend at a 45-degree angle (commonly called a lead angle) relative to one another. Octagonal inserts are particularly advantageous in that a single insert possesses a relatively large number of alternately usable cutting edges.
Round inserts also are known. Such an insert may be infinitely indexed since the circular shape of the insert eliminates the requirement for indexing the insert through a particular angle. In addition to conventional round inserts, there are so-called hollow ground round inserts. The cutting face of a hollow ground insert is dished or relieved so as to produce an extremely sharp (albeit somewhat fragile) cutting edge on the insert.
Other inserts which are less widely used are irregularly shaped inserts having four cutting edges which are separated from one another by non-cutting edges. The cutting edges of a given insert may be located at a particular lead angle such as a 15-degree lead angle or a 30-degree lead angle.
A significant challenge in the field of milling cutters is to remove material at a fast rate and with a milling machine of relatively low horsepower. Many small milling machines (e.g., those known as Bridgeport mills) are rated at 11/2 or 2 horsepower. In order to enable such machines to achieve a high rate of metal removal, it is necessary that the milling cutter cut through the metal in a relatively free manner.